How to show the attached image as the mkv thumbnail?

I have mkv files with covers attached to them. How do I get to show them (when they are there) as the thumbnails in my file manager instead of a random frame ffmpegthumbnailer is usually does? I know some distributions that have this set up. Is it possible to configure a .thumbnailer file to do this or is this bounded to a more 'bloated' file manager? I generally use Thunar, PCManFM and SpaceFM.